1. Field of the Invention
The invention pertains to a bridging clutch for installation in a hydrodynamic coupling device having a housing, a pump wheel, and a turbine wheel, wherein the clutch includes a torsional vibration damper with a drive element, a power take-off element, and a plurality of circumferential springs between the elements.
2. Description of the Related Art
A bridging clutch of this type is known from, for example, FIG. 2 of Japanese patent publication Sho 57-57,958 (1982). The bridging clutch is installed in the housing of a torque converter, which acts as a coupling device and which, as can be derived from the flow arrows in the drawing, is filled with a conveying medium in fluid form. The converter has a conventional hydrodynamic circuit, which is installed between a drive shaft and a transmission input shaft of a drive train, and contains not only a pump wheel and a turbine wheel but also a stator wheel installed axially between the other two wheels. The bridging clutch, furthermore, has a piston, which, when moved into a first axial position, can bring a friction element in the form of a plate into working connection with friction surfaces on the piston and on a ring-shaped abutment, and, when moved into a second axial position, can release this working connection. The friction element is mounted nonrotatably on an inner plate carrier, which is attached to the turbine shell of the turbine wheel and extends radially inward essentially parallel to the turbine wheel base, where the openings for circumferential springs and the actuating areas for the latter with which the plate carrier is provided allow it to serve as a part of the drive element of a torsional vibration damper. A hub disk serves as the takeoff element of the vibration damper, and it, too, is provided with openings and actuating areas for the circumferential springs. The hub disk is made as an integral part of a torsional vibration damper hub, which for its own part is centered nonrotatably on the previously mentioned transmission input shaft.
No measures are taken on the turbine wheel itself to center it with respect to the housing of the coupling device or with respect to the transmission input shaft, which means that the turbine wheel, which is held without any other radial support in the housing, is centered only by the circumferential springs of the torsional vibration damper.
According to FIG. 2 of the drawing of this Japanese patent publication, comparatively large axial distances are present between the inner plate carrier and the hub disk on the one side and between the latter and the turbine wheel base on the other side; these gaps allow the turbine wheel and the inner plate carrier mounted on it to shift axially. As a result of the prevailing pressure relationships, it can be assumed that, when the piston is in its working position, a chamber located axially between the piston and the converter cover has a positive pressure with respect to the hydrodynamic circuit, so that the piston will move the turbine wheel closer to the pump wheel by way of the friction element and the inner plate carrier. Conversely, when there is no pressure in the above-mentioned chamber, the pump wheel will be shifted axially together with the inner plate carrier and the friction element toward the piston because of the negative pressure then present. This makes it impossible to prevent a considerable amount of power from being lost as a result of drag.